Van der Waals forces

Definition

van der Waals forces are weak intermolecular attractive forces that arise between neutral molecules. These forces, while individually weak, can collectively contribute to the physical and chemical properties of substances.

5 Must Know Facts For Your Next Test

1. van der Waals forces are responsible for the condensation of gases into liquids and the solidification of liquids into solids.
2. The strength of van der Waals forces depends on the size and polarizability of the molecules involved, with larger and more polarizable molecules experiencing stronger attractions.
3. van der Waals forces play a crucial role in the conformations and folding of proteins, contributing to their overall three-dimensional structure.
4. The presence of van der Waals forces can influence the boiling and melting points of substances, as well as their viscosity and surface tension.
5. van der Waals forces are weaker than covalent and ionic bonds, but they can collectively contribute to the stability and properties of many chemical systems.

Review Questions

• Explain how van der Waals forces influence the conformations of ethane molecules.
  • The conformations of ethane molecules are affected by van der Waals forces, specifically London dispersion forces. In the staggered conformation of ethane, the hydrogen atoms are farther apart, minimizing the repulsive van der Waals interactions between them. Conversely, in the eclipsed conformation, the hydrogen atoms are closer together, resulting in stronger repulsive van der Waals forces and a less stable arrangement. The balance between these attractive and repulsive van der Waals interactions contributes to the preference for the staggered conformation of ethane.
• Describe the role of van der Waals forces in the stabilization of protein structures.
  • Van der Waals forces play a crucial role in the stabilization of protein structures, particularly in the maintenance of the three-dimensional folded state. The weak attractive interactions between the atoms and molecules within a protein, such as between non-polar side chains, contribute to the overall stability of the protein structure. These van der Waals interactions, along with other noncovalent interactions like hydrogen bonding and electrostatic interactions, help to hold the protein in its unique and functional three-dimensional shape. The collective strength of these van der Waals forces, acting in concert with other stabilizing interactions, is essential for the proper folding and functioning of proteins in biological systems.
• Analyze how the strength of van der Waals forces can influence the physical properties of substances, such as boiling and melting points.
  • The strength of van der Waals forces can directly impact the physical properties of substances, including their boiling and melting points. Substances with stronger van der Waals forces, such as those with larger and more polarizable molecules, will generally have higher boiling and melting points. This is because more energy is required to overcome the attractive van der Waals interactions and transition the substance from a liquid to a gas (boiling) or from a solid to a liquid (melting). Conversely, substances with weaker van der Waals forces will have lower boiling and melting points, as less energy is needed to disrupt the intermolecular attractions. This relationship between van der Waals force strength and physical properties is an important consideration in understanding the behavior and characteristics of various chemical substances.

Related terms

Dipole-Dipole Interactions: Attractive forces that arise between polar molecules with a permanent partial positive and partial negative charge.

Hydrogen Bonding: A special type of dipole-dipole interaction that occurs between a hydrogen atom bonded to a highly electronegative element and another highly electronegative element.

London Dispersion Forces: Temporary dipole-induced dipole attractions that arise due to the fluctuating distribution of electrons in atoms and non-polar molecules.